Tree frogs not good swimmers? Whaaaat? Ok, so some don't swim particularly well, like retf's, they just aren't built for it. But some, like cuban's and white's are not only good swimmers, they are superb swimmers. I kept my white's in a paludarium with 4" of water and they loved it! They spent a lot of time in the water and the tank ran at 78% humidity, so it's not like it was a lack of humidity drawing them there.
Bit large water features can be a royal pain in the butt. My suggestion is to plan it out thoroughly.
Why oh why would you want to add males? Your house not quiet enough? You hate sleep? Lol male white's call loud. And I mean loud! And at all hours of the night! Be careful what you wish for!! Lol
That was all I wanted to add. Eli and Amy have you pretty well covered otherwise
Education is the most powerful weapon we can use to change the world ~ Nelson Mandela